Effects of improved on-farm crop storage on perceived stress and perceived coping in pregnant women—Evidence from a cluster-randomized controlled trial in Kenya

Background Food insecurity can be harmful to pregnant women, as pregnancy is a challenging period with increased maternal nutritional requirements to ensure optimal fetal development and health of the mother. Whether food insecurity negatively affects maternal health may depend on how stressful pregnant women perceive this food insecurity to be and how strongly they believe they can cope with it. In Sub-Saharan Africa (SSA), pregnant women from smallholder households suffer from food insecurity due to post-harvest losses (PHL), i.e., loss of crops because of inadequate storage. An agricultural intervention that improves crop storage has been shown to reduce food insecurity. However, it remains to be determined whether this agricultural intervention (treatment) has an additional positive effect on pregnant women’s perceived stress levels and coping abilities. This study examines whether pregnant women from treatment households experience lower perceived stress levels and higher perceived coping abilities compared to pregnant women from control housholds. Methods and findings In a randomized controlled trial (RCT), short message service (SMS)-based mobile phone surveys were conducted to assess the causal effect of a food security intervention (improved on-farm storage of maize) on perceived stress and coping in pregnant women from smallholder households. Pregnant women were identified through these monthly surveys by asking whether someone in their household was currently pregnant. The significant results revealed that pregnant women from treatment households experienced more perceived stress but better perceived coping abilities compared to pregnant women from control households. Uncertainty due to lack of experience, this might have contributed to the higher perceived stress, as the women could not easily judge the benefits and risks of the new storage technology. However, the technology itself is a tangible resource which might have empowered the pregnant women to counteract the effects of PHL and thus food insecurity. Conclusion Our findings indicate that pregnant women from treatment households had higher perceived coping abilities but experienced more perceived stress. More research is needed on how this technology impacts maternal mental health in a broader sense and whether biological mechanisms, such as epigenetics, may underlie this association.


Background
Food insecurity can be harmful to pregnant women, as pregnancy is a challenging period with increased maternal nutritional requirements to ensure optimal fetal development and health of the mother. Whether food insecurity negatively affects maternal health may depend on how stressful pregnant women perceive this food insecurity to be and how strongly they believe they can cope with it. In Sub-Saharan Africa (SSA), pregnant women from smallholder households suffer from food insecurity due to post-harvest losses (PHL), i.e., loss of crops because of inadequate storage. An agricultural intervention that improves crop storage has been shown to reduce food insecurity. However, it remains to be determined whether this agricultural intervention (treatment) has an additional positive effect on pregnant women's perceived stress levels and coping abilities. This study examines whether pregnant women from treatment households experience lower perceived stress levels and higher perceived coping abilities compared to pregnant women from control housholds.

Methods and findings
In a randomized controlled trial (RCT), short message service (SMS)-based mobile phone surveys were conducted to assess the causal effect of a food security intervention (improved on-farm storage of maize) on perceived stress and coping in pregnant women from smallholder households. Pregnant women were identified through these monthly surveys by asking whether someone in their household was currently pregnant. The significant results revealed that pregnant women from treatment households experienced more perceived stress but better perceived coping abilities compared to pregnant women from control households. Uncertainty due to lack of experience, this might have contributed to the higher perceived stress, as the women could not easily judge the benefits and risks of the In Sub-Saharan Africa (SSA), food insecurity is particularly high among smallholder farming households, attributable to factors such as climate change-related extreme events and seasonality, which hamper agricultural production [24][25][26][27]. For example, a 10-day delay in the onset of the rainy season increases the risk of seasonal drought, thus affecting the food security status of smallholder farmers in SSA [28]. Furthermore, heavy rainfalls can prevent smallholder farmers from adequately drying their crops before storage, which can lead to increased moisture and thus mold growth during the storage period, rendering the crop inedible and therefore lost [29][30][31]. Extreme weather shocks, such as the aforementioned drought and rainfall, negatively affect crop production in Kenya [32] and are a major concern for smallholder farmers in rural Kenya [33]. Post-harvest losses (PHL) refer to the amount of crop lost due to factors such as crop handling and crop storage [31], with the latter accounting for the majority of PHL [34,35]. Indeed, a meta-analysis revealed that on average, 25.6% of harvested maize in SSA is lost due to insufficient crop storage [35]. A recent article states that the PHL of maize by storage pests amount to about 36% overall, with Western Kenya being the most affected [36]. Moreover, the lean season, i.e. a few months after the harvest, when food stocks are depleted and the coming crops were yet to be harvested, poses the challenge of maintaining food security in smallholder farming households [27,37], which can be further exacerbated by PHL.
Agricultural interventions that focus on PHL, a well-known contributor to food insecurity, may be helpful to counteract the negative effects of food insecurity on maternal mental health and the intergenerational adverse health effects for the offspring. One method to improve crop storage is the distribution of hermetic storage bags instead of conventional polypropylene bags. Hermetic bags have been shown to improve crop storage in Tanzania and thus reduce PHL significantly [38]. A reduction in food insecurity due to hermetic storage bags was also demonstrated among Kenyan smallholder farmers from the project described in the present study [39]. However, its effect on perceived stress and perceived coping (two components of the transactional stress theory) in pregnant women still needs to be elucidated.
In summary, on the correlation level, numerous studies have shown that food insecurity is associated with poorer mental health outcomes. We take this research forward by determine whether an agricultural intervention to improve food security (allocation and use of hermetic storage bags in households) can have beneficial mental health outcomes for pregnant women from smallholder households. We hypothesized that pregnant women in the treatment households would experience lower perceived stress and higher perceived coping as compared to pregnant women in the control households. Following the randomly allocated intervention, we collected perceived stress and perceived coping data over several months using monthly short message service (SMS)-based surveys. The treatment effects were analyzed via Intentionto-treat (ITT) analyses.

Study setting
The present randomized control trial (RCT) was conducted in Kakamega County, Western Kenya and included all 12 sub-counties of Kakamega and 59 out of 60 wards. Smallholder farming, and maize as the main staple food, are dominant in this Sub-Saharan region. The study area is affected by seasonality, with the lean season typically beginning around April or May and a secondary smaller harvest taking place around January or February [39]. A map of the study region and the smallholder farming groups' locations can be found in Huss et al. [39].

Research design and intervention
This study was embedded in a matched-pair, cluster-randomization design. Pair-wise matching of the farmers was performed using baseline variables such as food security and mean market distance [40]. After pairing, farmers were randomly assigned to the treatment or control group using spatial clustering. This resulted in 62 experimental clusters with 285 farmer groups (5 0 444 smallholder households). More detailed study information can be found in Huss et al. [39]. Of these 5'444 smallholder households, a subsample of 1,591 pregnant women took part in the present study.
The treatment group received five hermetic storage bags of the brand "AgroZ" per household and standardized training in their usage. Each bag has the capacity to store 100kg of maize. The intervention was implemented from 3 rd to 15 th September 2019 by our local partner International Centre of Insect Physiology and Ecology (icipe), with the training session developed by some of the authors of this paper. The control group continued storing their maize as usual-mostly in traditionally used polypropylene bags.

Outcome variable
The RCT was designed to assess the effects of the intervention (hermetic storage bags) on food security and a variety of health outcomes [41]. The present study focused on perceived stress and perceived coping, measured by the short form of the Perceived Stress Scale (PSS-4). The PSS is based on the stress theory of Lazarus [10,12] and measures the degree to which an individual perceives his/her life as stressful as well as the individual's perceived ability to cope with stress. The original version of the PSS consists of 14 items [42]; nowadays, a 10-item version is commonly used, and the scale has been further reduced to four items [43]. While some researchers found that the PSS-14, -10 and -4 capture two distinct psychological factors, coping and stress [44][45][46][47][48][49], others challenge this notion [50,51], particularly for the PSS-4 [52,53]. The PSS questionnaires have acceptable psychometric properties and have been validated in different countries (see review, [46]), as well as for pregnant women [54][55][56]. As the PSS-10 has been widely used to study Kenyan populations [23, [57][58][59][60][61][62], it is reasonable to assume that the PSS-4 can also be applied in Kenya. Our Kenyan partner icipe translated and back-translated the PSS-4 into Kiswahili and English (see S1 Table for the final translation of the PSS-4). We analyzed the PSS-4 data as two distinct psychological factors: The psychological factor "perceived coping" consists of items 2 and 3 of the PSS-4 and measures the perceived ability to cope with stress. The other factor, consisting of items 1 and 4, asks about the amount of stress the respondent is experiencing and is referred to as "perceived stress". Higher sum scores for the perceived stress factor indicate higher stress and higher sum scores for the perceived coping factor indicate a lower perceived ability to cope with stress. With regard to internal consistency in our data set, Cronbach's alpha for the one-factor model was less than 0.6 at 11 out of 12 measurement time points. For the two-factor model, the perceived stress factor had a Cronbach's alpha greater than 0.6 at eight out of the 12 time points and the perceived coping factor had a Cronbach's alpha greater than 0.6 at nine out of the 12 time points. Additionally, we analyzed the psychometric properties of the PSS-4 using a principal component analysis (PCA) for each measurement time point. The one-factor model explained a maximum of 47% of the variance while the two-factor model explained over 66% of the variance for each measurement time point (S2 and S3 Tables), thus supporting our choice of the two-factor model.

Data collection method
Throughout the RCT, the smallholder farmers received monthly SMS-based mobile phone surveys asking about their food security status [39]. Within these monthly surveys, the farmers were also asked whether someone in their household was currently pregnant. Farmers who answered "yes" to this question received an additional SMS-based mobile phone survey containing the PSS-4 questionnaire. Pregnant women could fill out the PSS-4 questionnaire via SMS-based survey every month while they were still pregnant. As soon as farmers answered "no" to the pregnancy question, they were excluded from the subsequent PSS-4 survey rounds. The observation period for this analysis was monthly from April 2020 until February 2021. The PSS-4 was seen as most suitable for use in SMS-based surveys as longer versions of the PSS are inefficient for repeated SMS-based surveys in larger populations in a developing country context [42]. For each completed survey round, participants received telephone credit (airtime) valued at 10 Kenyan Shilling. The treatment and control group received the same amount of airtime.

Research aim and statistical analysis
The purpose of this study was to determine whether an agricultural intervention consisting of an improved on-farm storage technology with hermetic storage bags affects the perceived stress levels and coping abilities of pregnant women in Kenyan smallholder households. As an alternative hypothesis, we also explore whether pregnant women in the treatment households have lower perceived stress and higher perceived coping abilities compared with pregnant women in the control households. Our null hypothesis is that there are no differences between perceived stress and coping by pregnant women in treatment and control households.
ITT analyses was used to analyze treatment effects (allocation and use of hermetic storage bags in the household) on perceived stress and perceived coping in pregnant women from smallholder farming households. ITT analysis is a recommended approach in RCTs when compliance and adherence to interventions cannot be guaranteed [63,64]. The ITT was estimated as the weighted average of the mean differences within pairs between treatment and control clusters [65] of pregnant women. For this purpose, arithmetic weights (wk) = n1k + n2k was used, representing the sum of the n observations in both clusters of each pair indexed by k. For further information see Imai and colleagues [65]. In addition, linear mixedeffects models was estimated for the entire observation period for both outcome measures, perceived stress and perceived coping, with the dichotomous variable treatment (yes/no) as the fixed effect and a random intercept that varied across the paired IDs (PID). Analyses were conducted using MATLAB and the open-source software R version 4.1.0 (the R Foundation for Statistical Computing, Vienna, Austria).

Ethics approval
Ethics approval was granted by the ETH Zurich Ethics Commission (EK, 2018-N-51) and icipe's Science Committee (no approval number used). Registration of the study design can be found in the American Economic Association (AEA) RCT Registry [41]. Informed written consent of the households to participate in the study was obtained before the start of the intervention.

Sample characteristics
During the observation period of April 2020 to February 2021, a total of 1,591 pregnant women from smallholder households participated in the SMS-based survey. Sample characteristics of baseline variables can be found in S4 Table. Baseline variables did not differ between control and treatment households, with the exception of slight differences in household size and age of household head. The households of the control group were slightly larger (M = 6.66, SD = 2.52) compared to those of the treatment group (M = 6.4, SD = 2.35) and the household heads of the control group (M = 45.21, SD = 12.78) were slightly older than the household heads of the treatment group (M = 44.14, SD = 12.35). However, these differences in household size (0.26) and age of household head (1.07 years) were very small.

Perceived stress and perceived coping in pregnant women from control households
In pregnant women in the control households, perceived coping scores were relatively stable during the lean season (between M = 4.4 and M = 4.6). After the end of the main harvest of 2020, perceived coping improved (lower mean values) for nearly all consecutive months (Fig  1). Perceived stress levels in pregnant women in the control households fluctuated over 12 consecutive months and were, overall, lower during the lean season. Compared to the lean season, pregnant women in the control households generally felt more stressed after the main harvest (Fig 2).

Impact of improved on-farm storage on perceived coping in pregnant women
For perceived stress and perceived coping, we expected the strongest treatment effects during the lean season when food stocks were depleted, which would then decrease after the start of the new storage period (the end of the main harvest). The results of the linear mixed-effects model show that pregnant women in the treatment households scored on average 0.167 points less than the control households on the coping measure over the entire observation period combined, which indicates higher perceived coping (t(6082) = -3.179, p = 0.001).
When analyzing each survey month separately, pregnant women in the treatment households perceived a higher ability to cope with stress in 11 out of 12 months compared to pregnant women in the control households (Fig 1). Perceived coping in pregnant women in the treatment households was significantly better during the lean season month of May 2020 (p = 0.014) and marginally better during the month of June 2020 (p = 0.094) (Fig 3). The difference between pregnant women in the treatment and control households was most substantial in September, right before the end of the main harvest of 2020 and the start of the new storage period, when pregnant women in the treatment households perceived themselves to cope significantly better with stress (p = 0.002). After the main harvest, pregnant women in the treatment households mostly continued to cope better with stress relative to the control group, although this difference was only significant in December 2020 (p = 0.005) (Fig 3). Supplementary S5 Table shows the ITT analysis for all survey months.

Impact of improved on-farm storage on perceived stress in pregnant women
Pregnant women in the treatment households scored an average of 0.13 points higher than those in the control households on the stress measure over the entire observation period combined, which indicates higher perceived stress (t(6082) = 2.314, p = 0.021).
When analyzing each survey month separately, pregnant women in the treatment households showed relatively stable perceived stress levels during the lean season, albeit higher compared to those in the control households (Fig 2). This difference was significant for the lean season months of May 2020 (p = 0.019), June 2020 (p = 0.004), August 2020 (p = 0.007) and September 2020 (p = 0.037) (Fig 4 and S6 Table). After the end of the main harvest in 2020, pregnant women in the treatment households more often felt less stressed than those in the control group, but this difference was only marginally significant for the month of January 2021 (p = 0.086).

Discussion
The present study is the first RCT to analyze the causal effect of a food security intervention on perceived stress and perceived coping (component of overall mental health) in pregnant women from smallholder farming households in SSA. Our results show that pregnant women from the treatment households had higher perceived coping scores but experienced more perceived stress compared to pregnant women from the control households.

PLOS ONE
Effects of on-farm crop storage on perceived stress and coping in pregnant women The implementation of the hermetic storage bags in the treatment households might have been evaluated as an externally determined environmental stressor that was uncertain, uncontrollable and threatening (primary appraisal), thus triggering a stress response. According to the results of the PSS-4 subscale perceived stress, pregnant women from the treatment households felt less able to control important things in their life and felt that difficulties were piling up so high that they could not overcome them (items 1 and 4) [42]. Previous research has demonstrated that participation in a new economic activity can initially increase psychological distress (measured using the PSS-10 as one factor) [66]. Hence, a lack of experience with this new on-farm storage technology, and uncertainty as to whether and how well these bags would work, may have contributed to the higher perceived stress levels in the treatment households.

PLOS ONE
Effects of on-farm crop storage on perceived stress and coping in pregnant women As individuals constantly interact with the environment, their cognitive processes (based on past experiences) can change. Therefore, after completion of the first harvest season and having gained the knowledge that these bags reduce food insecurity (adjusted primary appraisal), the significant effects of the treatment on perceived stress in pregnant women diminished and pregnant women in the treatment households therefore tended to be less stressed, albeit not significantly so. Moreover, the uptake of a new agricultural technology that targets food security may take longer to develop a positive impact on perceived stress. Stevenson et al. [67] measured how the implementation of an intervention to improve water quality for Ethiopian households affected psychological distress in Ethiopian women, and found no significant effect on psychological distress measured with the WHO Self-Reporting Questionnaire (SRQ-20). As a possible explanation for this finding, the authors suggested that the time between the implementation of the intervention and the stress measurement was too short to have yielded a potential treatment effect. Further research should implement longitudinal panel studies over several years to observe any effects.
Although the implementation of the new technology may pose a perceived threat, the technology itself is a tangible resource (secondary appraisal) that can be used to counteract the effects of PHL and therefore food insecurity. According to the subscale perceived coping of the PSS-4 [42], pregnant women in the treatment households felt more confident about their ability to handle personal problems and felt more that things were going their way (items 2 and 3) compared to pregnant women in the control households. In SSA, women are generally in charge of feeding the household. This forces them to actively overcome food insecurity by adopting different coping strategies such as stretching food resources and skipping meals [68, 69]. Given the higher perceived coping in pregnant women in the treatment households, one might assume that the intervention to reduce PHL empowered these women and gave them a tangible resource, as fewer food coping strategies were required [39]. Empowerment refers to "the process by which those who have been denied the ability to make choices acquire such an ability" [70]. Being deprived of basic needs reduces the ability to make meaningful choices [70]. Accordingly, it seems likely that pregnant women in the control households were deprived of choice over how to successfully feed their families, and this lack of empowerment attributable to food deprivation might have resulted in poorer perceived coping. This finding supports the social causation hypothesis that unfavorable environmental and economic conditions increase the risk of impaired mental health [71,72].
Mental health in pregnant women is affected by the time of gestation. Recent evidence indicates that the longitudinal course of distress during pregnancy exhibits a U-shaped curve [73], leading to the suggestion that the time of gestation might have impacted the effects of the treatment on perceived stress in our study. However, in contrast to observational studies, our study design reduces the risk of omitted variable bias as the matched-pair design rules out the influence of other potential confounding factors given that potential confounding factors should be similarly distributed in treatment and control households.
It is noteworthy that the timing of data collection coincided with the COVID-19 outbreak and COVID-19 restrictions imposed by the Kenyan government, which began in mid-March 2020 and continued until early July 2020. Focus group discussions with farmers in this RCT indicated that these restrictions had a strong impact on their daily lives, as farmers were unable to access agricultural markets, which in turn affected their food security status (for detailed information, see Huss et al. [39]). Specifically, Huss et al. [39] show that control households' food security declined significantly in the month following COVID-19 restrictions, and much more so than in treatment households. The agricultural intervention mitigated food insecurity among farmers in treatment households [39]. The mitigation of the food shock in treatment households is consistent with our findings that the intervention enables these households to better cope with sudden food shocks. We presume that these effects are randomly distributed among the pregnant women in our study because, to our knowledge, the study region in which our farmer households are located was similarly affected by the COVID-19 crisis. However, it is not possible to systematically disentangle the effect of the intervention and the effect of COVID-19 on our outcome variables.
Some limitations need to be acknowledged when interpreting the findings reported in this study. First, the questionnaire was completed via self-report. However, as there was no personal interaction with the pregnant women, we do not expect a systematic response bias [74]. Second, we cannot guarantee that the pregnant women answered the SMS-based surveys themselves, although to minimize this potential problem we requested in our survey that the PSS-4 should be answered by the pregnant women. Third, it may have been preferable to use a stress questionnaire that better represents the cultural background of the study population, since perceived stress in the PSS-4 might not adequately reflect the local understanding of stress, namely "thinking too much" [75][76][77][78].

Conclusion
This study set out to determine whether improved on-farm storage has positive effects on stress perception and perceived coping abilities among pregnant women from smallholder farming households in Kenya. Results show that pregnant women from treatment households had higher perceived stress levels but also higher perceived coping abilities than pregnant women from control households. The findings suggest that the use of hermetic storage bags in Kenyan smallholder households provides pregnant women with a sense of empowerment to counteract the effects of PHL and thus food insecurity. Further research could examine the long-term effects of this intervention over several main harvest seasons to determine whether perceived stress levels decrease from one main harvest season to the next as pregnant women gain more experience and confidence in using this new storage technology. In addition, future research should focus on how this storage technology impacts maternal mental health in a broader sense and whether biological mechanisms, such as epigenetics, may underlie this association. Such findings could have important implications for countries in SSA, where women in rural areas are strongly affected by food insecurity and mental health problems [79], and could contribute to the achievement of the second and third goals of the United Nations Agenda for Sustainable Development [80], namely to end food insecurity and ensure well-being and mental health, not just for women but also for their offspring.
Supporting information S1